Various means have been used in prior art military applications to detect the presence and depth of penetration of an enemy intruder into a given land area. These devices are used to activate an explosive device so that it will have maximum lethal effect against an enemy. One of the problems commonly associated with devices utilizing seismic sensing has been the device's ability to cope with tremendous signal strength variations which are generally generated as a function of differing soil propagation conditions and changing target speed. When this problem is applied to the requirement of target sensing, it frequently causes very large variations in the detection range of a seismic sensor. In addition, variations in intruder size and speed coupled with changing soil conditions have been found to cause variations in sensing range of 20 to 1.